1. Field of the Invention
The present invention relates to transmitting/receiving systems and methods, transmitting apparatuses and methods, receiving apparatuses and methods, and programs used therewith. In particular, the present invention relates to a transmitting/receiving system and method in which, when stream data is encrypted while key updating is performed in a predetermined updating period, the updating period is shortened as much as possible, a transmitting apparatus and method, and receiving apparatus and method used with the system and method, and a program used therewith.
2. Description of the Related Art
In recent years, a first encryption technique (see, for example, Japanese Unexamined Patent Application Publication No. 2003-143548) has been proposed and its use has been discussed. The first encryption technique prescribes that, when stream data including a plurality of consecutive unit data items is sequentially encrypted for each unit data item, keys used when the unit data items are encrypted are updated on the basis of predetermined rules.
Also, realization of a transmitting/receiving system has been discussed. The transmitting/receiving system includes a transmitting apparatus for encrypting stream data in accordance with a first encryption technique and transmitting the encrypted data to a different apparatus, and a receiving apparatus as the different apparatus for receiving the encrypted data and decrypting the encrypted data in accordance with a first decryption technique corresponding to the first encryption technique.
In addition, it is necessary for this transmitting/receiving system to transmit, from the transmitting apparatus to the receiving apparatus, a plurality of keys used when first encrypted data is generated. Accordingly, it has been discussed that, after the keys have been encrypted one by one in accordance with a second encryption technique, the encrypted keys are transmitted from the transmitting apparatus to the receiving apparatus.
In this embodiment, in order for the receiving apparatus to decrypt a predetermined portion (such as a predetermined unit data item) in the encrypted data (obtained by encrypting the stream data), it is necessary to prepare a key (corresponding to the predetermined portion) used for encrypting the predetermined portion. Specifically, before initiating decryption of the predetermined portion, the receiving apparatus needs to beforehand decrypt second encrypted data including an encryption key corresponding to the predetermined portion by using a second decryption technique corresponding to the second encryption technique.
Therefore, the updating period of the key is dependent on a processing time necessary for encryption and decryption in the second encryption technique (second decryption technique). Accordingly, for example, when the second encryption technique, whose processing time is approximately several seconds, is employed, approximately one minute is employed as the updating period of the key, in consideration of security.